Two new compounds, (+)-rumphiin (3) and polyalthurea (7), together with seven known ones, 3,4,5-trimethoxy benzoic acid (1), (-)-seselinone (2), cannabisin D (4), allantoin (5), oxostephanine (6) and a mixture of beta-sitosterol (8) and stigmasterol (9) were isolated from the stems of Polyalthia rumphii. The chemical structures of 3 and 7 were elucidated by the combination of spectroscopic data, and the absolute configuration of 3 at C-2 was determined by the matrix method to be R. All compounds were evaluated for their cytotoxicity on four human cancer cell lines, which demonstrated that 3 was a moderate bioactive lignan, and 6 showed significant anticancer activity against SPC-A-1 and BEL-7402 cell lines with IC50 values of 1.47 and 1.73 microg/mL, respectively.